1. Field of the Invention
This invention generally relates to integrated circuit (IC) fabrication and, more particularly, to an erbium-doped silicon (Si) nanocrystalline embedded Si oxide (SiOx) waveguide and an associated fabrication method.
2. Description of the Related Art
The evolution of semiconductor industry in the last several decades has largely relied on scaling down the minimum feature size of IC devices, in which metal (copper and aluminum alloys) thin films are used as interconnects for electrical signal transmission. However, as aggressive scaling continues, metal interconnects are a problem in keeping pace with the ever increasing speed and power consumption of IC devices. One solution to this problem utilizes optical interconnects, which rely upon photons instead of electrons for on-chip and chip-to-chip communication. Flat panel displays, which are fabricated primarily on glass substrates, face similar challenges as well, as more and more functions and devices are being added on the glass panels. In additional, the flat panel display industry faces the challenges of metal interconnects within a panel, as the panel development continues increasing beyond Generation 8. The use of optical interconnects can decrease interconnect delays and power consumption, and increase device speed in IC devices and flat panel displays.
It is known to use optical fiber as an active medium for optical signal amplification in Erbium-doped fiber amplifiers (EDFAs) for long-distance communication. However, optical fiber cannot be integrated into ICs using conventional processes. External light sources can be fabricated using III-V compound semiconductors for applications on Si-based IC devices. However, these materials require extra, non-conventional fabrication steps. As such, hybrid assemblies still dominate the optoelectronics assembly process, to connect optoelectronics devices to Si-based IC devices.
Silicon dioxide (SiO2) has potential as an optical waveguide material since it exhibits minimum attenuation near 1540 nanometers (nm), which is the most widely used wavelength in long-distance optical communication. A SiO2 waveguide can be fabricated on Si wafers and glass display panels using conventional Si-compatible process that are widely available. Another attractive feature of SiO2 is that once doped with Erbium ions (Er+) at the proper levels, it can convert light to a wavelength of 1540 nm, which coincides with the wavelength of minimum attenuation for optical signals in an SiO2 medium. Thus, optical signals in this wavelength range can either be transmitted further from a light source, or with less power, through the same length of SiO2 waveguide.
However, as an indirect semiconductor Si has been long considered as a poor light-emitting material. In recent years, Si-nc (nanocrystalline) embedded Si-rich Si oxide (SRSO) has been found to have promising light-emitting properties. The optimal emission wavelengths of Si-nc SRSO as fabricated by conventional methods typically ranges from ˜600 nm to ˜900 nm. Adding Er+ ions in Si-nc embedded SRSO films shifts the emission wavelength of the combined material from being centered near 900 nm, to 1540 nm, and increases the quantum efficiency of the emission significantly. The Si-nc particles work as sensitizers to excite Er+ ions in Si oxides matrix.
There are no known processes that are able to fabricate Si nanocrystalline SRSO film on temperature sensitive substrates such as glass, which cannot be heated over a temperature of about 650° C.
It would be advantageous if optical waveguides operating at 1540 nm could be fabricated using low-temperature Si-based IC fabrication processes.